1. Field of the Invention
The present invention pertains to a device and method for protecting and sealing exposed wires, particularly wires which make up electrical harnesses used in automobile engines.
2. Brief Description of the Background Art
Dimensionally-recoverable tubing is commonly used to protect spliced wires within electrical harnesses in the automobile industry. One of the preferred splice configurations is a xe2x80x9cstub splicexe2x80x9d. In a stub splice, each wire to be spliced has its electrically insulative covering removed at one end, to expose bare electrically conductive wire, with all of the bare wires to be spliced arranged to run in the same direction. The exposed bare wires are essentially parallel to each other at one end of the configuration. The bare wires are then crimped, welded or soldered together to form a xe2x80x9cnuggetxe2x80x9d. Subsequently, the nugget must be protected and sealed from the external environment. A preferred means for protecting the nugget and sealing out moisture and other contaminants is to encase the nugget in a dimensionally-recoverable tubing which has a sealant/adhesive coating interior to the tubing. Typically, heat is applied to cause the sealant/adhesive to flow, while simultaneously causing the tubing to heat-recover (shrink) about the nugget. The tubing shrinks around the end of the exposed wires and the adhesive/sealant flows within the tubing to cover the exposed wires. The adhesive/sealant also flows along the wires to contact and cover a portion of the unstripped, electrically insulative wire covering. This provides a seal over the entire length of the exposed wires up to and including the beginning of the insulative wire covering.
However, during installation, the adhesive/sealant used in combination with the dimensionally-recoverable tubing tends to act as a lubricant, causing the tubing to slide or back off of the inserted wires. Typically, the tubing does not completely slide off the wires, but this may happen on occasion. This phenomenon is known as xe2x80x9cmilk-offxe2x80x9d. When milk-off results in a substantial back off of the tubing from the inserted wires, (for example, the tubing has backed off of the inserted wires by more than about one third of the recoverable tubing length), the stub splice may not be sealed properly, and moisture can reach the exposed wires, causing a short. Further, if the adhesive/sealant available for sealing becomes significantly reduced in quantity due to leakage from the closure end of the tubing or due to being left on wires which are no longer enclosed by the tubing as a result of milk off, there may be inadequate adhesive/sealant to protect the exposed portion of the wires enclosed by the tubing.
A short may also occur if a strand of wire which is part of the nugget is bent up and pokes through the wall of the heat-shrinkable tubing while it is being recovered (at this time the tubing is hot and softened).
As is readily apparent, an electrical short within the wiring harness of the engine compartment of an automobile or other motor vehicle is not only inconvenient when the vehicle stalls, but may be dangerous to the driver and passengers of the vehicle.
The prior art contains a number of devices which have been designed to provide protection of electrical wiring splices from the elements, and in particular from moisture penetration, which tends to be one of the worst problems. Some examples of these prior art devices are described below. U.S. Pat. No. 3,984,912, issued Oct. 12, 1976 to Johnston et al., discloses a method for splicing cable in which electrical wire conductors which project from two insulated cable end portions are received in tubular electrical connectors which have been electrostatically precoated with electrical insulating material. Each precoated connector end portion respectively abuts and is sealed in engagement with insulation on an associated cable end portion. The precoated connectors are crimped so that they grip the wire conductors to form a basic electrical splice. A tubular inner melt liner and a tubular outer sleeve of thermoplastic electrical insulating material surround the basic splice. Heat is applied to simultaneously melt the inner liner and shrink the outer sleeve to encapsulate the basic splice.
U.S. Pat. No. 4,528,419, issued Jul. 9, 1985 to Charlebois et al., discloses a method of forming an encapsulated splice region between two cable ends. After end portions of the core have been exposed beyond the jacket and sheath or shield, the conductors are splayed outwards and the cable end portions are brought close together. Splices are then formed between conductors of the two cables and the conductors are folded over either one cable jacket or the other to locate each splice upon and supported by the jacket.
Each splice is individually covered with sealing material, and end regions of the cables are encapsulated so as to encapsulate the splices and to seal them so that they are fluid-tight. Heat is provided during the encapsulation of the splices in order to soften the sealing material so that it will completely surround each splice.
U.S. Pat. No. 4,849,580, issued Jul. 18, 1989 to Reuter et al., discloses a closure/sealant combination for use in providing an xe2x80x9cenvironmental sealxe2x80x9d around a wire junction or splice. The preferred embodiment of the closure has a unitary construction comprising an outer, openable shell having an internal biasing mechanism. Viscous sealant material is positioned within the closure such that the biasing mechanism forces sealant material around a junction to be sealed and, in particular, between adjacent wires in such junctions.
U.S. Pat. No. 4,863,535, issued Sep. 5, 1989 to More, discloses a method and arrangement for generating an environmental seal around a connection such as an electrical junction. The arrangement comprises a pad arrangement which is in association with a substrate and a sealant pad. The sealant pad comprises a highly viscous sealant which, under pressure, can be forced into areas between adjacent wires to provide effective moisture seals. According to a preferred method of the invention, a substrate having sealant on it is folded around a junction to be sealed, such that the substrate retains the sealant against the electrical junction. Pressure is applied to the enclosed sealant pad, generating hydraulic forces in such a manner as to direct the sealant against the electrical junction.
U.S. Pat. No. 4,963,700, issued Oct. 16, 1990, to Olsen et al., discloses a closure for providing an environmental seal about a wire junction. The closure comprises a closable shell defining, when closed, an internal wire junction receiving chamber having first and second opposite open ends for receiving wires. The shell comprises first and second shell sections, and an interference fit locking arrangement is oriented between the shell sections. The shell sections may be unitary (ie., joined along a hinge line), or they may be independent of one another, but engageable in a nesting manner. The interference locking mechanism preferably comprises a plurality of elongate, continuous, interengageable ratchet teeth. In use, sealant material is positioned within the shell sections, and a junction to be sealed is placed within the shell.
U.S. Pat. No. 4,974,042, issued Nov. 20, 1990, to Seabourne et al., and assigned to the assignee of the present invention, discloses a blocking arrangement for suppressing fluid transmission in cables, particularly for use in harnesses for automotive applications. The arrangement comprises a generally flat blocking array that is formed from a fusible polymeric sealant (e.g., a hot-melt adhesive or a thermosetting adhesive). The blocking array has a number of passageways for receiving wires of the cable. The passageways extend from one end of the array to the other. The assembly includes a heat-shrinkable covering that can be positioned around the blocking array in its flat configuration and recovered about the array by application of heat. The sealant is capable of melting during recovery of the covering and being forced from a generally flat configuration to a generally cylindrical one by recovery of the covering.
U.S. Pat. No. 5,221,885, issued Jun. 22, 1993 to Bostock et al., and assigned to the assignee of the present invention, discloses a device and method for forming a solder connection between a plurality of electrical conductors. The device comprises a hollow, dimensionally heat-recoverable sleeve that contains a quantity of solder. The sleeve has at least one open end to allow insertion of one or more electrical conductors. A deformable retaining member is located within the sleeve. The retaining member is mechanically deformable to retain the conductors in the desired alignment within the sleeve, and is deformable while in contact with the conductors.
U.S. Pat. No. 5,378,855, issued Jan. 3, 1995 to Delalle, and assigned to an international subsidiary of the assignee of the present invention, discloses a device for forming an electrical connection at the end of a bundle of wires. The device comprises an electrically insulating, preferably heatshrinkable, sleeve; a metallic connecting element located within the sleeve; and a quantity of solder for forming a permanent electrical connection between the conductors. The connecting element has a tapering internal surface which has a screw thread, so that a temporary electrical connection can be formed by screwing the bundle of wires into the connecting element. Preferably, the connecting element is formed by winding a wire into a frusto-conical form. Wire bundles may be spliced using a device in which the connecting element has a pair of internally threaded portions into which different cable bundles can be screwed.
U.S. Pat. No. 5,441,560, issued Aug. 15, 1995 to Chiotis et al., discloses a crimp splicer comprising a connector, an insulating sleeve, and a gel or encapsulant. The connector is preferably cylindrical or barrel-shaped and consists of a ductile metal which is a good conductor or capable of being deformed with a crimping device. The insulating sleeve is generally cylindrically shaped and has a bore formed therein which runs the length of the sleeve. The sleeve is shaped and sized to enable mechanical retention of the connector disposed within the bore of the sleeve. Suitable materials for the sleeve include nylon and polyvinylidene fluoride, since the necessary crimping force can be applied through these materials without damage to the insulating sleeve or loss of retention of the connector. The gel is an organopolysiloxane gel composition.
As can be observed by looking through the patents described above, the various devices proposed are relatively complex and expensive to manufacture. In some cases, where the device requires crimping, application of too much or too little pressure may result in a device which does not function properly.
The stub splice which was described above, protected by dimensionally-recoverable tubing with an interior adhesive/sealant provides for ease of application, harness manufacturing simplicity, and is relatively inexpensive when compared to other devices. Thus, if the reliability problems which may arise due to milk-off and poke-through of wire strands could be eliminated, this splice configuration would be highly advantageous.
Applicants have created an improved device and method for protecting from the elements wires which have a portion of their electrically insulative covering stripped off, such as spliced wires, and particularly stub-spliced wires. The improved device prevents the milk-off and wire poke-through previously described, while simultaneously reducing the possibility that (due to loss of adhesive/sealant during application of the device) there will be inadequate adhesive/sealant to provide a proper seal.
Accordingly, disclosed herein is a device for protecting and sealing wires having an exposed portion where an electrically insulating covering is stripped off. The device comprises (a) a dimensionally-recoverable tubing, (b) a layer of sealant (which preferably also acts as an adhesive) applied to at least a portion of the interior surface of the tubing, and (c) a cap or sheath into which at least a portion of the exposed wires are inserted, wherein at least a portion of the cap or sheath is positioned interior to the dimensionally-recoverable tubing. The cap or sheath includes a configured interior shape for holding the inserted wires, and is designed to permit the adhesive/sealant to flow around the inserted wires. The cap or sheath typically forms a closure at one end of the dimensionally-recoverable tubing or is positioned at or adjacent to a closure end of the tubing. At least the exterior, and preferably all of the cap or sheath is made of non-conductive material. The device can be used to protect and seal exposed wires in bundles, such as the nuggets of a stub splice, of varying diameters, depending on the design of the configured interior shape of the cap or sheath.
Also disclosed herein are several embodiments representative of the kind of a cap or sheath which is useful as part of the device described above. The critical elements of the cap or sheath are that it include a configured shape for holding the wires; that the configured shape permit a sealant/adhesive to reach the exposed portion of the wires and the juncture of the exposed portion with the portion having the electrically insulative covering, in a manner which is sufficient to provide a moisture-resistant sealing of the wires; and that the cap or sheath be constructed of a material which prevents wire poke through during the recovery of the dimensionally-recoverable tubing.
A portion of the cap may act as the closure end of the device, having a shape which is easily grasped by automated handling equipment, with a configured shape for holding the wires extending from the cap portion which acts as the closure end.
The configured shape may be in the form of fins which are positioned longitudinally along the length of the cap or sheath and which extend radially toward the interior of the cap or sheath. The fins may be positioned longitudinally along the length and extending at an angle to the radius and toward the interior of the cap or sheath. The configured shape may include directional arms or barbs which, after the wires have been inserted, make it difficult to remove the wires from the cap or sheath. The configured shape may be in the form of an internal coil or spiral located within the cap or sheath, wherein the coil extends along the longitudinal direction of the cap or sheath. Preferably, the opening dimension inside the coil decreases from the entry to the cap or sheath toward the end of the cap or sheath nearest the closure end of the protective device. Preferably, the fins, arms, coil, or other configured shape is injection molded or extruded as an integral part of the cap or sheath.
Also disclosed herein is a method for protecting and sealing exposed wires, wherein the method involves the use of the protective device described above. The first step of the method comprises inserting wires, a portion of which are exposed (do not have an electrically insulating covering thereon) into the protective device a sufficient distance so that a configured shape within the device can grasp and hold the ends of the exposed wires inserted therein, wherein the protective device comprises (a) a dimensionally-recoverable tubing, (b) a layer of sealant (which preferably acts as an adhesive) applied to at least a portion of the interior surface of the tubing, and (c) a cap or sheath into which at least a portion of the exposed wires are inserted, wherein at least a portion of the cap or sheath is positioned interior to the dimensionally-recoverable tubing, and wherein the cap or sheath includes a configured interior shape for holding the inserted wires, which shape is designed to permit the adhesive/sealant to flow around the inserted wires.
The second step of the method involves treating the device in a manner which causes the dimensionally-recoverable tubing to recover. Preferably, the dimensionally-recoverable tubing is heat-recoverable tubing, and the tubing is exposed to a temperature sufficient to shrink or to recover the tubing and to cause the adhesive/sealant to flow within the tubing. The adhesive/sealant has a viscosity ranging from about 100 poise to about 10,000 poise, and preferably from about 500 poise to about 5,000 poise, at the time it flows within the tubing. Further, the cap or sheath must maintain sufficient strength at the heat-recovery temperature to prevent wire poke-through from the exposed wires held by the cap or sheath.